The present invention relates to the technical field of adsorptive materials and in particular to adsorptive filters which can be used, for example, to clarify fluids, such as gas/air streams.
More particularly, the present invention relates to an adsorptive filter medium based on a plurality of a first filter element and also on a plurality of a second filter element other than the first filter element, wherein the filter medium possesses an optimized adsorption behavior and/or optimized adsorption kinetics, particularly with regard to the breakthrough behavior of chemical and/or biological poison/noxiant materials, such as warfare agents.
The present invention further relates to methods of using the filter medium according to the invention for sorptive, in particular adsorptive, applications and/or for the removal of noxiants, specifically gaseous noxiants, or of gases or substances that are toxic, harmful and/or environmentally damaging.
The present invention also relates to filters and filter materials obtained using at least one filter medium of the present invention and/or comprising at least one filter medium of the present invention.
Fluids/fluidic media, more particularly gases, gas streams or gas mixtures, such as air for example, are often clarified or purified in the prior art using particulate systems based on particles possessing specific activity (e.g., adsorbents, ion exchangers, catalysts, etc). The prior art discloses for instance the use of adsorber particles to remove poisonous or noxiant agents and odors from gas or air streams, including in particular in the field of NBC protection.
The use of loose beds of the aforementioned particles, particularly in the form of loose granular-bed filters, is a significant use form to bring the particles concerned, such as adsorber particles for example, into contact with the fluid to be clarified.
Since small particles, such as adsorber particles for example, have a larger surface area in relation to their diameter than comparatively large particles, it is only to be expected that the performance is better with the comparatively small particles. However, small particles in a loose bed lead to a pressure drop that is high and not controllable as such, and also promote the formation of channels within the bed, causing a heightened risk of breakthrough with regard to the poisonous/noxiant agents to be adsorbed. This is why the particle size used in loose beds is often only a compromise, so the particle sizes that are actually optimal for a particular application can usually not be employed. More particularly, the need to achieve economical operating conditions, in particular an acceptable pressure drop, means that larger particles (e.g., adsorber particles) often come to be employed than would be desirable for optimal utilization of the adsorption efficiency and for an optimized breakthrough behavior—i.e., the time until the substances to be removed appear in a critical amount/concentration at the filter outlet—and so it is often the case that a considerable portion of the theoretically available capacity cannot be utilized.
In this context, DE 36 24 975 C2 describes a packed-bed filter based on a shaft which is packed with a granular bed and the side walls of which are pervious to the medium to be filtered, wherein a belt system moves/displaces the packed bed transversely to the direction of throughflow of the gas mixture to be clarified. The system described therein is disadvantageous in that it is cumbersome and hence unsuitable for compact filter systems and in that filter efficiency is not always optimal because of the packing used for the adsorption material.
It is further known in the prior art for the particles employed to remove odors and poisonous/noxiant agents from fluidic media, e.g., adsorber particles, to be secured/attached to a carrier in order thereby to reduce the resulting pressure drops of the filter system, especially compared with beds. However, in-service/on-stream time is occasionally shortened for filter systems of this type. More particularly, the breakthrough behavior with regard to the substances to be adsorbed/removed is problematic with filters of this type, which is extremely critical particularly in the case of highly toxic substances, such as chemical and/or biological poisons/noxiants, since even very small amounts of the substances in question have drastic consequences for the health/life of people confronted therewith. Prior art filters of this type, wherein the adsorption material is fixed to a carrier structure, do generally have a low flow(through) resistance, but, in the use state, the concentration profile within the filter of the noxiant/poisonous agents to be removed has a propensity due to dispersion effects in particular to excessively spread apart in the main flow direction of the fluid/gas mixture to be clarified, leading to a reduced breakthrough time and hence to inferior in-service/on-stream times for the filter.
DE 40 20 246 A1 discloses a device for adsorbing gases from an air stream and/or a carrier gas using an adsorbent bed suitable for fluidization, wherein the adsorbent particles employed therein are further additionally fixed to a downstream carrier in the manner of a fixed bed, the pressure drop of the fixed bed in the use state being stated to be low. The device described therein has an overall large volume due to the fluidization zone provided and occasionally has the disadvantage that particles fluidized in the use state may cause plugging of the fixed bed and that an optimal (initial) breakthrough behavior is not always ensured with regard to noxiant/poisonous agents in particular.
DE 38 13 564 A1 and the same patent family's EP 0 338 551 A2 disclose an activated carbon filter layer for NBC respirators which comprises a highly air-pervious, substantially shape-stable three-dimensional carrier scaffold whereto a layer of granular, specifically spherical activated carbon particles is fixed, wherein the carrier scaffold may be a braid formed of wires, monofilaments or struts, and/or a foam-based structure. However, the system described has not been optimized in particular with regard to a prolongated breakthrough behavior for substances/gases to be removed/adsorbed, such as biological and/or chemical noxiants/poisons.
DE 43 43 358 A1 further discloses porous bodies comprising activated carbon which consist of plates and agglomerates formed by ground activated carbon incorporated in a porous SiO2 matrix. What is more particularly described therein are porous plates or bodies having adsorbing properties wherein activated carbon granules or activated carbon spherules and/or particles comprising activated carbon are adhered together by means of a silicate solution and subsequently the silicate bridges are converted into silica gel bridges and the resultant bodies are dried. One disadvantage with this is the fixed geometry of these porous bodies and also their lack of flexibility and compressibility, making them unsuitable for filtering applications under mechanical loading. A further disadvantage is that the particles comprising activated carbon are completely wetted with the silicate solution, so a large proportion of the capacity of these particles is no longer available for adsorptive processes. The system described has further not been in any way optimized with regard to the breakthrough behavior of chemical/biological noxiants/poisons.
In conclusion, therefore, the filter systems known in the prior art do not always have good pressure drop properties nor optimal in-service/on-stream times, especially not with regard to the removal/adsorption of highly toxic substances from gas/air streams, so the systems known in the prior art are not always optimally suitable for an industrial-technical employment and/or for employment as a sheet filter and/or respiratory filter in the field of NBC protection in particular. The filter systems of the prior art often have a but minimal adsorption capacity, and the adsorption kinetics are also occasionally not optimal, so to compensate that in a corresponding manner occasionally requires large volumes/amounts of adsorbents, yet this leads to a further deterioration in the pressure drop properties and is also prejudicial to compact filter design/construction.